1,721,101 research outputs found
Action of soil humic matter on plant roots: Stimulation of ion uptake and effects on(Mg2++K+) ATPase activity
No full textThe effects of soil humic matter on the uptake of ions by oat roots and on the (Mg2++K+) ATPase activity, responsible for energy transduction for ion transport at cell membrane, were studied. Four-day-old roots treated for 8 h with unfractionated humic solution (50 μg org C × ml-1) took up K+ and SO4staggered-2 ions at rates, respectively, 33% and 106% higher than the controls. Similar effects were caused by humic and fulvic acids, and by the hot-acid soluble and hot-acid insoluble fractions prepared from humic acids. At org C concentration higher than 1 μg ml-1, the humic extract inhibited both Mg2+ dependent and K+-stimulated ATPase activities of microsomes isolated from roots. At 0.33-1 μg org C ml-1, the Mg2+-dependent activity was inhibited, whereas the activity stimulated by K+ increased. Humic acids and the acid-insoluble fraction inhibited the ATPase activity more than fulvic acids and the acid-soluble fraction. Preliminary results of SDS - PAG electrophoresis of membrane proteins showed two polypeptides associated with membrane of humus treated roots, which where absent in the control. Differences between the two phenomena and structure-activity relationships will be discussed. © 1987
The rhizosphere as a site of biochemical interactions among soil components, plants and microorganisms
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Sucrose accumulation in developing peach fruit
No full textUptake of C-14-sugars and activities of sucrose metabolizing enzymes were determined in order to study the mechanism(s) of sucrose accumulation in developing peach fruit. Mesocarp of young peach fruit contained glucose and fructose but little sucrose. Starting 88 days after anthesis (DAA) the sucrose concentration increased greatly. The mechanism of sucrose accumulation was studied by measuring C-14-sucrose and C-14-glucose uptake rates at three different stages of fruit development, and by assaying weekly the activity of enzymes involved in the hydrolysis and/or synthesis of the soluble sugars. Uptake of 0.5-100 mM C-14-sucrose and C-14-glucose by mesocarp tissue slices showed a complex pattern at the first stage of fruit development (62 DAA). During the subsequent growth stages the pattern of sugar uptake changed and was approximately monophasic at the third stage of fruit development.
At 10 mM, glucose was taken up more rapidly than sucrose at the first and second stage of fruit development. Uptake was partially inhibited by the uncoupler carbonyl-cyanide m-chlorophenylhydrazone (CCCP) at 25 mu M. These results, together with the presence of a putative extracellular invertase, suggest an apoplastic route for sucrose uptake which is dependent, at least in part, on energy supply.
Activities of sucrose hydrolyzing enzymes (insoluble acid invertase, soluble acid invertase, neutral invertase, sucrose synthase) were high in young fruits and declined sharply with fruit development concomitantly with accumulation of sucrose. The storage of the sugar was not accompanied by a rise in synthetic activities (sucrose synthase, sucrose phosphate synthase), suggesting that sucrose could, at least in part enter the carbohydrate pool directly
Iron deficiency induces the expression of a specific plasma membrane H+-ATPase gene in cucumber
No full textWater-extractable humic substances as nutrient acquisition signals for root hairs development in Arabidopsis
No full textEffect of NO3-, Cl- and DIDS on H+-ATPase of plasma membrane vesicles isolated from maize roots
No full textHeterogeneity of plasma membrane H+-ATPase isolated from apical and subapical maize root segments
No full textSoil humic substances affect transport properties of tonoplast vesicles isolated from oat roots
No full textThe effect of a low molecular size (<5 KDa) humic fraction, essentially fulvic acids, on microsomal and tonoplast ion-stimulated ATPase activity was studied. After 20 min of pre-incubation with microsomal vesicles from oat roots, humic substances at organic C concentration of up to 0.5 μg cm-3 increased KCl-stimulated ATPase activity, while they inhibited enzyme activity at higher concentrations. Cl--stimulated ATPase activity of tightly sealed tonoplast-enriched vesicles was similarly affected by <5 KDa humic substances. This behaviour was not observed when gramicidin D was added to the assay medium. Proton transport by vesicles incubated up to 5 min with <5 KDa humic molecules was affected in a concentration-dependent manner, strongly resembling that observed for ATP hydrolysis, whereas it was severely reduced when the assay conditions were close to those used for measuring ATP hydrolysis (20 min pre-incubation of vesicles with humic substances). The transmembrane electrical potential was negatively affected, irrespective of the concentration of humic molecules. Furthermore, a 15-min pre-incubation strongly reduced the formation of a potential gradient. The size and concentrations of humic substances employed make an interaction with the vacuolar membrane of root cells plausible. The results show that the main target of humic molecules is the electrical membrane potential and suggest a possible way of interference of these naturally occurring substances with the biochemical mechanisms involved in plant mineral nutrition. © 1992 Kluwer Academic Publishers
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